Synthesis of unsaturated bicyclic hydrocarbons



United States Patent 3,407,239 SYNTHESIS OF UNSATURATED BICYCLICHYDROCARBONS Nazzareno Cameli, Milan, Gaetano Censolo, Ferrara, and

Guido Sartori and Alberto Valvassori, Milan, Italy, as-

signors to Montecatini Edison S.p.A., Milan, Italy, a

corporation of Italy No Drawing. Continuation of application Ser. No.490,079, Sept. 24, 1965. This application Sept. 25, 1967, Ser. No.670,460

Claims priority, application Italy, Sept. 25, 1964, 20,661/64 11 Claims.(Cl. 260-666) The present invention relates to an improved method forthe synthesis of unsaturated bicyclic hydrocarbons with condensednuclei. This application is a continuation of Ser. No. 490,079 filedSept. 24, 1965, and now abandoned.

More particularly the present invention relates to an improved methodfor the synthesis of hydrocarbons having the general formula in which Rand R are the same or different and may be hydrogen atoms or methylgroup.

These hydrocarbons, as is known, are obtained by reacting according tothe Diels-Alder reaction a cyclic diene, more particularlycyclopentadiene, with an acyclic conjugated diolefin, more particularlybutadiene, isoprene or dimethylbutadiene.

Rather low yields of pure product have been obtained previously since,together with the mixed dimers, large amounts of homodimers, highboiling products and solid products are also obtained.

By operating at temperatures of about 145 C. cyclopentadieneprevailingly behaves as a diene while the acyclic diolefins prevailinglybehave as dienophilic compounds. Thus endocyclic compounds are obtainedhaving the structural Formula I and, in a minor amount, compounds havingthe Formula II in which R and R are hydrogen atoms or methyl groups.

By operating at temperatures higher than 180 C., on the other hand, theacyclic diolefin prevailingly behaves as a diene and cyclopentadieneprevailingly behaves as the dienophilic compound. In this case thecompound of type (II) prevails.

The necessity of operating at such high temperatures in order to obtaincompounds of this last type, however, leads to an increase in theformation of polymer and of homodimers, resulting in non-profitableconsumption of the starting compounds.

The formation of homodimers also leads to another disadvantage which isparticularly remarkable in the case of the reaction betweencyclopentadiene and isoprene. In this case, the desired product, 6methyl 4,9,7,8 tetrahydroindene and the homodimers of cyclopentadieneand isoprene have nearly the same boiling point and it is thereforedifficult to obtain the desired pure compound.

3,407,239 Patented Oct. 22, 1968 It has now been found according to thepresent invention that it is possible to substantially reduce some ofthe aforementioned disadvantages and to completely eliminate otherdisadvantages, with an increase in the yield of pure products.

It is also possible to use as strating material not only cyclopentadienebut also dicyclopentadiene or mixtures of these two hydrocarbons withoutdetrimentally influencing the final results.

According to the present invention the co-dimerization ofcyclopentadiene, dicyclopentadiene or mixtures of both compounds withconjugated acyclic diolefins including butadiene, isoprene anddimethylbutadiene is carried out by an improved process in which:

.(a) The reaction is carried out in the presence of a solvent,

(b) The monomers to be co-dimerized are introduced into a reactionvessel preheated to a temperature between and 250 0., preferably betweenand 250 C.

(c) At least a part of the reaction product obtained from thedimerization reaction is subjected to pyrolysis at a temperature between300 and 900 C. The reaction product before the pyrolysis includes thedesired unsaturated bicyclic compounds together with the compounds oftype (I), the unreaeted starting monomers, homodimers formed from thestarting monomers, polymers and other high boiling point products andlow boiling point products including the diluent inert solvent. As aresult of the pyrolysis the starting monomers are obtained together withthe codimers.

The compounds of type (I) disappear completely during the pyrolysis. Bycarrying out the codimerization within the preferred temperature rangeof from 150 and 250 C., the ratio between compounds of type I andcompounds of type II, decreases down to about 0 with increasingtemperature values. This constitutes a particular advantageous featureof the process of the present invention. However, even when thecompounds of type I are present in the reaction mixture they disappearby virtue of the pyrolysis.

By carrying out the reaction in the presence of a solvent, the formationof polymer is substantially reduced.

As solvents, various types of inert compounds can be used such asaromatic aliphatic or cycloaliphatic hydrocarbons having from 5 to 10carbon atoms. For example, n-heptane, n-octane, benzene, toluene,xylene, cyclohexane may be used.

By introducing cyclopentadiene, dicyclopentadiene or mixtures thereofand the aliphatic diene into the reaction vessel preheated to thedesired reaction temperature, a further reduction in the amount ofpolymer and of homodimer is obtained.

The reaction product or the residues obtained from distilling thereaction product to remove low boiling point fractions is then subjectedto heating, for example, by passing it through a quartz tube filled withquartz rings. The tube can be inserted into an electrically heatedfurnace and a slight depression applied to it in order to facilitate theremoval of the vapors formed by pyrolysis.

The pyrolysis may be carried out in one or two steps. In the first steptemperatures of between 300 and 500 0., preferably of between 350 and450 C. are used.

The residue obtained from the first pyrolysis step, after distillationof the low boiling products (HP. 200 C.), may then be subjected to asecond pyrolysis and preferably between 500 and 900 C. A furtherrecovery of the starting monomers is thus obtained.

If the pyrolysis is carried out in a single step the temperatures rangebetween 300 and 500 0, preferably between 350 and 450 C.

The pyrolysis step results in the formation of mixed dimer together withthe starting reactants, cyclopentadiene and aliphatic diene. This resultmay be due in part to depolymerization. These starting reactants may befed again to the reaction vessel. An almost complete absence of lowboiling decomposition products and of carbon residues is observed afterthe pyrolysis step.

As mentioned above, either the entire reaction product obtained from thedimerization reaction or the residues obtained from distilling off thelow boiling point fractions may be subjected to the pyrolysis step.However, the process can be conveniently shortened and improved bydirectly charging into the pyrolysis tube the reaction mass obtainedfrom the dirncrization step Without first distilling off the low boilingpoint fractions.

The gas chromatographic analysis of the reaction mass after pyrolysisshows the complete absence of dicyclopentadiene, which has beenmonomerized to cyclopentadiene and of the band corresponding to thecompound of the type (I), which has been in part isomerized to compound(II), and in part decomposed into the starting monomers.

According to another characteristic of the process according to thepresent invention, by carrying out the reaction in the presence of anexcess of cyclopentadiene, dicyclopentadiene or mixtures thereof withrespect of the stoichiometric amount required to form compound (II), theamount of homodimers of the aliphatic diene is re inarkably reduced.Molar ratios of cyclopentadiene, dicyclopentadiene and mixtures thereofto aliphatic diene of from 2:1 to 5:1 are preferred. Thedicyclopentadiene excess present in the reaction mass is then completelyrecovered as cyclopentadiene in the subsequent pyrolysis. An excess oflinear diolefin leads to a great amount of the corresponding polymers,which are difiicult to pyrolize. Thus an excess of linear diolefinresults in a lower conversion rate.

It should be stressed that under the synthesis conditions according tothe present invention, substantially the same results are obtained bystarting either from cyclopentadiene, from dicyclopentadiene or frommixtures thereof.

Another important fact, as regards the economy of the process, is thepossibility of using both as solvent and as monomer feed petroleumcracking fractions containing one or both of the monomers required forthe synthesis. In this case the addition of an extraneous diluentsolvent is not necessary as it is present in the petroleum crackingfraction.

The reaction may be carried out under atmospheric pressure or aboveatmospheric pressure. It is preferable to operate in an autoclave underautogenous pressure. The pressure in this case will depend on thetemperature and on the composition of the reaction mixture. Pressuresabove 20 atmospheres are generally not used.

As regards the reaction times, it has been observed that under thesynthesis conditions according to the present invention times between 30minutes and 4 hours are sufiicient, when the temperatures ranges from150 to 250 C. The conversion of aliphatic diene under the preferredreaction conditions amounts to 85% after 30 minutes and to 96% after 60minutes.

The reaction may be carried out in the presence of a polymerizationinhibitor so as to prevent the alphatic diolefin from polymerizing. Asinhibitors, tert. butyl catechol and other phenols such as hydroquinonemay be used.

The process may be conveniently carried out either batchwise such as inan autoclave, or continuously, for example, by passing the reactingsubstances through a suitably sized tubular reactor.

The following examples illustrate the invention but are not to beconstrued as limiting its scope.

Example 1 2. g. of hydroquinone and 1,200 cm. of benzene are introducedin a 3-litre autoclave under a nitrogen atmosphere. The whole is heatedto 190 C. and, when this temperature is reached, 330 g. of isoprene(4.85 mols) and 320 g. of cyclopentadiene (4.85 mols) are 4 charged. Theautoclave is agitated at a temperature of 190-200 C. for 2 hours and 30minutes.

The discharged cold mass from the autoclave is subjected todistillation, first under atmospheric pressure, in order to removebenzene, and then under vacuum. 428 g. of liquid phase and 220 g. ofresidue are thus obtained. By quantitative chromatographic analysis, theliquid phase appears to consist of 327.8 g. of6-methyl-4,9,7,8-tetrahydroindene, g. of homodimers and 11.2 g. of5-isopropenyl-norbornene.

The 220 g. of residue are slowly dropped into a quartz tube filled withquartz rings, inserted in a vertical oven. The diameter of the quartztube is 3 cm. and the height of the packing is 45 cm. The reaction iscarried out at 400 C. under a pressure of 350 mm. Hg. The vapors formedare condensed at the tube outlet in a vessel cooled with methanol andDry Ice.

The 214 g. of discharged product, when subjected to distillation,consists of 14.5 g. of isoprene, 39 g. of cyclopentadiene, 33 g. of6-methyl-4,9,7,S-tetrahydroindene and 127.5 g. of residue.

This residue is slowly dropped into a quartz tube with an inner diameterof 3 cm. filled with copper wire to a height of 10 cm., and maintainedat a temperature of 720730 C. under a pressure of 2 mm. Hg. 118 g. ofproduct containing 20 g. of isoprene, 20 g. of cyclopentadiene and 78 g.of high boiling liquid are obtained.

The total yield of methyl tetrahydroindene with respect to convertedisoprene therefore is 62%.

Example 2 1 g. of hydroquinone and 300 cm. of benzene are introducedinto a 2-litre autoclave. The autoclave is heated to 190 C. and, whenthis temperature is reached, 80 g. of dicyclopentadiene and 82.5 g. ofisoprene are charged. The autoclave is kept in agitation at atemperature of 190-200 C. for 2 hours and 30 minutes.

The discharged cold mass from the autoclave is freed of benzene bydistillation. The residue of this distillation is then introduceddropwise into the tube described in Example 1 and under the sameconditions. From g. of mass charged into the tube 158 g. of a mixtureconsisting of 7 g. of isoprene, 36 g. of cyclopentadiene, 20 g. ofisoprene homodimers, 76.7 g. of 6-methyl-4,9,7,8- tetrahydroindene and18.3 g. of residue are obtained.

The yield of methyltetrahydroindene with respect to converted isopreneis 53%.

Example 3 2. g. of hydroquinone and 1,200 cm. of benzene are introducedinto a 3-litre autoclave under a nitrogen atmosphere. The autoclave isheated to C. and, when this temperature is reached, 365 g. (5.5 mols) ofcyclopentadiene and 166 g. (2.45 mols) of isoprene are charged. Theautoclave is kept in agitation at a temperature of 190200 C. for 2.5hours.

The cold mass discharged from the autoclave is freed of benzene bydistillation. The residue from this distillation is then introduceddropwise into a quartz tube with a diameter of 3 cm. filled with quartzrings. The packing zone has a height of 75 cm. and is heated by avertical electric oven. The reaction is carried out at a temperature of400 C. under a pressure of 650 mm. Hg. From 529 g. of mass charged inthe tube, 524 g. of a mixture consisting of 17 g. isoprene, 243.8 ofcyclopentadiene, 20 g. isoprene homodimers, 198 g. of 6-m'ethyl-4,9,7,8tetrahydroindene and 45.2 g. of residue are obtained.

The yield of methyl tetrahydroindene with respect to converted isopreneis 67%.

Example 4 1 g. of hydroquinone and 590 cm. of benzene are introducedinto a 2-litre autoclave under a nitrogen atmosphere. The whole isheated to 190 C. and, when this temperature is reached, 238 g. (3.6mols) of cyclopentadiene and 49 g. (0.72 mol) of isoprene are charged.The autoclave is kept in agitation at a temperature of.190- 200 C. for 2hours and 30 minutes.

. .The cold mass discharged from the autoclave is freed of benzene bydistillation. The residue from this distillation is then introduceddropwise into an electrically heated quartz tube. The height of thepacking and the pressure and temperature conditions are identical withthose described in Example 3. From 285 g. of mass charged in the tube280 g. of a mixture consisting of 4.7 g. of isoprene, 185.5 g. ofcyclopentadiene, 3.74 g. of isoprene homodimers, 67 g. of6-methyl-4,9,7,8-tetrahydroindene and 18.76 g. of residue are obtained.

The yield of methyltetrahydroindene with respect to converted isopreneis 74%.

Example 1 g. of hydroquinone and 590 cm. of benzene are introduced intoa 2-litre autoclave under a nitrogen atmosphere. The whole is heated to190 C. and, when this temperature is reached, 237 g. (1.795 mols) ofdicyclopentadiene and 49 g. (0.72 mol) of isoprene are charged. Theautoclave is kept in agitation at a temperature of 190 200 C. for 2hours and 30 minutes.

The cold mass discharged from the autoclave is slowly introduceddropwise into an electrically heated quartz tube. The height of thepacking and the temperature and pressure conditions are identical withthose described in Example 3. From 794 g. of mass charged in the tube,785 g. of a mixture consisting of 510 g. of benzene, 1.5 g. of isoprene,170 g. of cyclopentadiene, 10.3 g. of isoprene homodimers, 70 g. of6-methyl-4,9,7,8-tetrahydroindene and 23 g. of residue are obtained.

The yield of methyltetrahydroindene with respect to converted isopreneis 74%.

Example 6 129 g. of cyclopentadiene and 200 g. of a C fraction ofpetroleum cracking, containing 56.7 g. of isoprene are introduced into al-litre autoclave containing 1 g. of hydroquinone, pre-heated to 190 C.The autoclave is kept in agitation at a temperature of 190200 C. for 2hours and 30 minutes.

The cold mass discharged from the autoclave is slowly introduceddropwise into an electrically heated quartz tube. The height of thepacking, the temperature and pressure conditions and the operations areidentical with those described in Example 3. From 320 g. of mass chargedin the tube, 309 g. of a mixture containing 69 g. of 6-methy1- 4,9,7,8-tetrahydroindene and 19 g. of residue are obtained.

The yield of methyltetrahydroindene with respect to the isoprene chargedis 61%.

Example 7 1 g. of hydroquinone and 1,000 cm. of benzene are introducedinto a 3-litre autoclave under a nitrogen atmosphere. The whole isheated to 190 C. and, when this temperature is reached, 264 g. ofcyclopentadiene and 330 g. of dimethylbutadiene are charged. Theautoclave is kept in agitation at a temperature of 190-200 C. for 3hours and 30 minutes.

The cold mass discharged from the autoclave is subjected todistillation, first under atmospheric pressure to remove benzene andthen under vacuum. 351 g. of liquid phase and 263 g. of residue are thusobtained. The liquid phase appears to consist of dicyclopentadiene (66g.) 5,6- dimethyl-4,9,7,S-tetrahydroindene (188 g.) anddimethylbutadiene homodimer (77 g.).

The 263 g. of residue are slowly introduced dropwise into anelectrically heated quartz tube. The height of the packing, thetemperature and pressure conditions and the operations are identicalwith those described in Example 3.

55 g. of cyclopentadiene, 25 g. of dimethylbutadiene, 24 g. of5,6-dimethyl-4,9,7,8-tetrahydroindene, 16 g. of dimethylbutadienehomodimer and 139 g. of residue are collected.

Example 8 Example 9 100 g. of C fraction, 0.05 g. of tert. butylcatecholand 8.8 g. of cyclopentadiene are introduced into the same autoclave ofExample 1. The molar ratio between isoprene and cyclopentadiene is 1:1.The procedure of Example 7 is then repeated.

The analysis of the products is reported in Table 1.

TABLE I Example 8 Example 9 Grams, Grams, Grams, Grams, percent percent;percent percent before after before after reaction reaction reactionreaction Saturated hydrocarbons having 4-6 C atoms 37. 6 36. 9 33. 7 33.9 Olefimc compounds having 4-6 0 atoms 33.9 34. 1 31. 1 31.3 Butadiene2. 3 0. 2 2. 1 0. 2 Piperylene- 8. 1 3. 1 8. 15 3. 3 Isoprene 13. 2 0. 812. 1 0. 8 1-4 pentadiene 0. 7 0. 3 0. 64 0.3 Cyclopentadien 4. 4 O. 14. 4 0. 1 Isoprene dimers-.. 2. 5 2. 7 Cyclopetadiene dimers 0. 6 8.2 1. 8 G-methyl-tetrahydroindene CIEPLV 5. 0 9. 5

7-methyl-tetrahydroindene Tetrahydroindene Example 10 1 g. ofhydroquinone and 317 cm. of benzene are introduced into a l-litreautoclave under a nitrogen atmosphere. The whole is heated to 190 C. andwhen this temperature is reached, 54 g. of butadiene and 132 g. ofdicyclopentadiene are added. The autoclave is kept in agitation at atemperature of l200 C. during 2 hours and 30 minutes.

The mass discharged is distilled at first under atmospheric pressure inorder to eliminate benzene and then at 20 mm. Hg 80 g. of a liquid phase(B.P. 4070 C.) and 100 g. of a high boiling residue. The liquid phasecontains 4,9,7,8 tetrahydroindene (48 g.), vinylcyclohexene (7, 2 g.),dicyclopentadiene (15 g.) and 2-vinyl-norbornene (5 g.).

The 100 g. of the high boiling residue, obtained after distillation ofthe liquid phase are introduced dropwise into a quartz tube electricallyheated. The conditions of the pyrolysis are the same as those describedin Examples 3. g. of product consisting of 35 g. of cyclopentadiene and60 g. of high boiling residue are obtained.

7 Example 11 The codimerization is carried out as in Example 5. The rawreaction product is introduced dropwise into a quartz tube, the lowerportion of which is provided with a refrigerator connected with twovessels connected in series.

The second vessel is connected with a vacuum pump. The pyrolysis iscarried out at 400 C. and 350 mm. Hg. The refrigerator and the firstvessel are kept at 85 C. by means of a circulation of hot water: thesecond vessel is cooled to 78 C. The composition (in percentage byweight) of the mixture collected in the two vessels is as follows:

8 least a portion of the thus obtained reaction product to pyrolysis ata temperature of from 300 to 900 C.

2. The process according to claim 1, in which all of the product of saidreaction between the cyclodiene and acyclic diolefin is subjected topyrolysis.

3. The process according to claim 1, in which the portion of thereaction product which is subjected to pyrolysis is the residueremaining after distilling off the low-boiling point fraction of saidreaction product.

4. The process according to claim 1, in which the inert solvent ispreheated to 150-25 0 C.

5. The process according to claim 1, in which the pyrolysis is carriedout at 35 0-450 C.

Product collected in the first vessel 165 g. Product collected in thesecond vessel 620 g.

Obviously, other modifications may be made in carrying out the inventionwithout departing from the spirit thereof, and therefore we intend toinclude in the scope of the appended claims all variations which will beapparent to those skilled in the art from the disclosures made, andillustrative examples given, herein.

What is claimed is:

1. A process for the synthesis of unsaturated bicyclic hydrocarbons withcondensed nuclei having the general formula in which R and R areselected from the group consisting of hydrogen and the methyl group,comprising preheating a solvent selected from the group consisting ofaromatic, aliphatic and cycloaliphatic hydrocarbons to a temperature offrom 80 C. to 250 C., introducing into the solvent maintained at thetemperature in the range 80 C. to 250 C., a cyclo-diene selected fromthe group consisting of cyclopentadiene and dicyclopentadiene andmixtures thereof, and an acyclic conjugated diolefin selected from thegroup consisting of butadiene, isoprene and dimethylbutadiene, to formthe said unsaturated bicyclic hydrocarbon of the formula given byreaction of said cyclo-diene and said acyclic diolefin at a temperatureto which the solvent is preheated, and then subjecting at 6. The processaccording to claim 1, characterized in that the said reaction is carriedout under atmospheric pressure.

7. The process according to claim 1, characterized in that the saidreaction is carried out above atmospheric pressure.

8. The process according to claim 1, in which the molar ratio betweensaid cyclo-dienes and the acyclic diolefin is from 2:1 to 5:1.

9. The process according to claim 1, characterized in that the pyrolysisis performed in two steps, the first pyrolysis step being performed at atemperature of from 300 C. to 500 C., and the second pyrolysis stepbeing performed at a temperature of from 500 C. to 900 C.

10. The process according to claim 9, in which the second pyrolysis iscarried out between 500 and 900 C.

11. The process according to claim 1, in which the reaction is carriedout in the presence of a polymerization inhibitor.

References Cited UNITED STATES PATENTS 2,752,406 6/1956 Segfried 260-6663,110,739 11/1963 Bimber 260-666 3,183,249 5/ 1965 Wiese 260-666 DELBERTE. GANTZ, Primary Examiner.

V. OKEEFE, Assistant Examiner.

1. A PROCESS FOR THE SYNTHESIS OF UNSATURATED BICYCLIC HYDROCARBONS WITHCONDENSED NUCLEI HAVING THE GENERAL FORMULA